Taphrenalla Pholyotha & Panha, 2021

Pholyotha, Arthit, Sutcharit, Chirasak, Tongkerd, Piyoros, Jeratthitikul, Ekgachai & Panha, Somsak, 2021, Integrative systematics reveals the new land-snail genus Taphrenalla (Eupulmonata: Ariophantidae) with a description of nine new species from Thailand, Contributions to Zoology 90 (1), pp. 21-69 : 47-49

Genus Taphrenalla Pholyotha & Panha , gen. nov.

Type species. Nanina (Macrochlamys) diadema Dall, 1897

Etymology. Taphrenalla is derived from ‘ Taphr ’ (the Greek word ‘ Taphros ’) meaning ‘trench or ditch’ and ‘ enalla ’ (the Greek word ‘ enallax ’) meaning crosswise. Therefore, the generic name means the snail with transverse ditches or radial grooves on the shell sculpture. The gender of the new generic name is feminine.

Description

Shell. Shell dextral, depressed to globosely depressed, thin, translucent, corneous to dark brown colour. Shell surface shiny, smooth (fig. 4A), with very fine growth lines or sculptured, very weak (fig. 4B) to strong (figs 4C, D) radial grooves starting from suture. Suture shallow impressed (figs 4A, B), deep impressed (fig. 4C), or wide and deep channel-shaped (fig. 4D). Whorls 5–6, increasing regularly. Last whorl rounded to slightly shouldered. Aperture crescentic with simple lip. Columellar margin simple and little expanded near umbilicus. Umbilicus perforate, narrowly opened.

Genital organs. Genitalia with short to long penis; thick or thin penial sheath. Epiphallic caecum usually straight, rarely a little bent at tip (not spirally coiled); penial retractor muscle attached to head of epiphallic caecum (rarely attached near the head). Flagellum relatively short and enlarged at base. Penial verge well-developed and small to large; penial caecum usually present and short or rarely absent. Female genital organ well-developed; dart apparatus located on vagina or at vagina and penis junction. Spermatophore long, needle-shaped and translucent. Head filament smooth, shorter than sperm sac and gradually thinning to terminal point. Sperm sac enlarged, capsule-shaped and contained whitish sperm mass. Tail filament very long and thin tube; region close to sperm sac bearing one or two spines.

Radula . Teeth arranged in U-shape with very wide angle. Central tooth symmetrical tricuspid; mesocone lanceolated-shaped; ectocones short and located at middle of tooth height. Lateral teeth asymmetrical tricuspid; mesocone triangular shaped; endocone smaller than ectocone; ectocone located below endocone. Marginal teeth with obliquely bicuspid, elongate and narrower teeth, and outermost teeth shorter and smaller than inner teeth (fig. 4H).

External features. Living snails usually covered with reticulated skin; three colourful stripes running from head to tail (one at middle of body and two on each side of body near foot sole). Eye stalks and head usually with dark colour; tail region usually with lighter colour than head region. Pallial cavity and some internal organs visible through translucent shell (figs 4F, G).

Mantle collar large, well developed and composed of two shell lobes and three dorsal lobes (figs 4E–G); shell lobes usually slender and longer than dorsal lobes. Right shell lobe placed on upper shell surface and longer than left shell lobe placed below periphery. Right dorsal lobe larger than left dorsal lobe; left dorsal lobe divided into anterior left dorsal lobe and posterior left dorsal lobe. Foot sole tripartite; caudal foss long and narrow; caudal horn raised and large. Colouration of soft body usually variable from reddish, orange, yellow, milky-white to greyish, and colour disappeared in preserved specimens.

Figure 4 Schematic of shell sculpture, mantle lobes, body terminology and radular of Taphrenalla gen. nov. A–D. radial grooves and suture types on upper shell surface: A. no radial grooves with shallow impressed suture. B. weak to nearly absent radial grooves with impressed suture. C. deep radial grooves with deep impressed suture. D. deep radial grooves with wide and deep channel shaped suture. E. dorsal view of mantle collar. F. right-hand side of snail shows mantle lobes and colour stripes on body. G. left-hand side of snail shows mantle lobes. H. representative SEM images of radular.

Distribution range. Endemic to Malay Peninsula: Southern Thailand ( fig. 1 ) and probably in Peninsular Malaysia.

Remarks. Taphrenalla diadema is the type species of the new genus because this species somewhat represents the morphology in general among congeneric species and is also the oldest valid species. Although the absence of radial grooves is evolved in T. zemia sp. nov. and T. alba sp. nov., they present the other characteristics of yellowish stripes on the body and a simple spermatophore. The spermatophore of T. alba sp. nov. has two spines near the sperm sac but is spineless in other regions. In addition, the molecular analysis grouped them within the Taphrenalla clade with strong support.

For comparison with the other closely related ariophantid genera, Taphrenalla gen. nov. can be distinguished from Sarika , Macrochlamys , Taphrospira , Syama , and Rasama by the shell sculpture having radial grooves, while the others have a smooth shell without radial grooves ( table 5 ). The shell morphology of Hemiplecta and Cryptozona are clearly different from the new genus in being much larger, with a smooth shell surface and without a radial groove. Regarding the genitalia anatomy, Taphrenalla gen. nov. have a penial verge, dart apparatus, and straight or slightly bent epiphallic caecum. Compared to the other genera, Macrochlamys and Syama both have a spirally coiled epiphallic caecum, but only Syama has no dart apparatus. The genus Taphrospira also has a straight epiphallic caecum and is without a dart apparatus, while the genus Rasama has neither an epiphallic caecum nor a dart apparatus (Blanford & Godwin-Austen, 1908; Schileyko, 2002, 2003). Thus, the genitalia of the genus Sarika is similar to Taphrenalla gen. nov. However, all species of the genus Sarika , except for S. consepta (Benson, 1860) , have no penial verge (Pholyotha et al., 2020), while this character is present in all Taphrenalla species. The taxonomic status of S. consepta is needed to be investigated in the future using a molecular approach.

In addition, most Taphrenalla species have bright body colouration patterns of the left, middle, and right stripes, either restricted to the head section or running from head to tail, while all Sarika species have a monochrome greyish to blackish body colour (Pholyotha et al., 2020).

Figures

Figure 1 Map showing the sampling sites of the 11 Taphrenalla species along Southern Thailand.Each colour of the distribution range follows the phylogenetic tree of all Taphrenalla species in fig.3.